Bill, W4ZV wrote:
Over flat terrain, a dipole up ~1/2 wavelength
has 7-8 dB gain over a vertical at typical 30
degree takeoff angles. On a mountain top, the TOA
goes down because the effective height is raised.
---------------------------------------------------
When people say "vertical", they usually mean a 1/4 wavelength (or less)
radiator. Such verticals are HUGELY dependent upon the ground return for
their efficiency. There's been an on-going argument about that since Marconi
hisself was tinkering with them, but that standard for comparison is that a
1/4 wave radiator should have something on the order of 50 to 100 0.2 wave
radials if it's going to be comparable of a 1/2 wave radiator. That's not to
say an vertical is always inefficient, but that one can't really assess how
efficient it is when using other ground systems and locations. The only
exception to that is a vertical over salt water, as in at sea on a ship.
Short of such a massive ground system, a decent comparison with a horizontal
1/2 wave radiator can only be made with a vertical 1/2 wave radiator (or at
least with radiators of the same physical length if both are less than 1/2
wave).
Even then there will be huge differences based on the propagation involved,
although on HF it's far less than VHF and above. On HF,
reflection/refraction of the wave in the ionosphere pretty well rotates and
mixes the polarization.
Ron AC7AC
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